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Occupational Noise

Published: 01st Mar 2012 in OSA Magazine

hearing protectionPerhaps the most pervasive and widespread occupational hazard in industrialised nations around the world is high levels of noise. Noise is defined as unwanted sound, sound interfering with or masking another sound, or sound occurring at irregular intervals varying in intensity and frequency.

Occupational noise is an underestimated hazard. Noise induced health effects are considered an emerging environmental burden of disease by the World Health Organization (WHO). Exposure to noise not only causes noise induced hearing loss (NIHL); it is a contributing factor to numerous non-auditory health outcomes.

Noise exposure at levels below hearing damage criterion induces adverse health outcomes. Non-auditory health endpoints such as annoyance, cognitive impairment, psychosocial changes, physiological stress reactions, endocrine imbalance, and biochemical changes leading to hypertension and ischemic heart disease are just as debilitating as NIHL. Significance of these biochemical changes is dependent upon the degree they affect health, wellbeing, and performance.

Workers are exposed to complex, intermingled combinations of environmental stressors. Difficulty differentiating health effects of noise from other environmental effects has hindered research efforts.

Too few systematic studies of the effects of low level noise have been completed, and most have looked at acute rather than chronic effects. Noise exposure has been poorly characterised; quality and quantity of data is not consistent for all health outcomes.

Noise induced health effects do not follow toxicological principles of dosage. Exposure-response relations are clearly defined for NIHL, and can be demonstrated for some non-auditory effects, but are not fully understood.

A clear, mechanistic pathway between noise and damage to the auditory system is biologically obvious and generally accepted. Scientific evidence showing a strong association between NIHL and effects of occupational noise that increase with magnitude and duration of noise exposure supports this link.

Yet mechanistic pathways for non-auditory health effects are elusive and the exposure-response relationship has not been demonstrated for all effects.
Perception of noise is subjective and introduces bias, leading to skewed results. Studies are prone to bias if confounding factors are not effectively controlled by experimental design or statistical methods. Drug and alcohol use, smoking, gender, age, occupation, diet and nutrition, and stress reducing activities can impact results. Future studies must use improved methodology that considers potential confounding factors.

Noise sensitivity

Approximately one in five people are acutely sensitive to noise, and sensitivity tends to increase with age, above average intelligence and socio-economic status. Noise sensitivity is a vulnerability factor for psychiatric disorders and is highly correlated with neuroticism. Noise sensitive individuals are likely to experience greater stress and annoyance in response to noise exposure.

Noise annoyance

According to WHO, health is a state of complete physical, mental, and social wellbeing. Very little doubt exists that annoyance from noise adversely affects wellbeing.

Noise induced annoyance is defined as “a feeling of resentment, displeasure, discomfort, dissatisfaction or offence which occurs when noise interferes with someone’s thoughts, feelings, or daily activities.”.

Noise is perceived as annoying, intrusive, and harmful to one’s health, often causing fear, mild anger, helplessness, depression, anxiety, withdrawal, dissatisfaction agitation, or exhaustion. Annoyance is proportional to the degree of interference caused by noise. Typically, annoyance manifests a response, such as closing a window or door when outside noise is perceived to be too loud. Noise is more likely to be considered annoying when it’s random, higher pitched, or occurs at night. Warmer environmental temperatures also tend to increase annoyance levels.

Threshold of annoyance may be dependent on presence of background noise. In a quiet environment, noise at much lower levels may be perceived as annoying. With background noise present, the threshold of annoyance is higher because the noise has to rise above the level of the background noise to be perceived.

Although subjective due to individual noise sensitivity, defining annoyance levels helps quantify noise. Intensity alone does not account for degree of annoyance; the person’s attitudes and beliefs concerning the source of the noise are major determinants.

hearing protectionWho is affected?

Certain sectors of the population with pre-existing conditions are more vulnerable to noise. Prolonged exposure is suspected of leading to cumulative effects, even small changes in blood pressure may have adverse health effects on at-risk segments of the population.

Research suggests noise induced health effects are gender specific. Males experience higher accident and sick leave rates, higher job dissatisfaction, and higher post-work irritability than females. All psychological distress symptoms except depression are higher for females. Noise exposure can reduce the pace at which females work. Shift work increases all effects of noise, both auditory and non-auditory.

Occupational noise is associated with most types of work activities. Some occupations, including manufacturing, transportation, mining, construction, and the military are linked to higher risks of developing NIHL and other adverse health outcomes.

Today’s workplace duties have shifted from sensorimotor tasks to verbal tasks; many workers now inhabit offices rather than working all day on a production line. Handheld devices, ringing phones, conversations of others, and ventilation systems are sources of distracting noise in the office.

Surprisingly, office workers exposed to low levels of noise experience musculoskeletal disorders attributed to poor posture.

Job satisfaction and performance

Workforce retention substantially reduces rising costs of training new employees. Employees exposed to lower levels of noise exhibit more loyalty and have a stronger sense of company attachment. Most choose to remain with the company longer than those working in a noisy, distracting environment. Workers often base job satisfaction on perceived noise levels.

• Increased noise levels = decreased job satisfaction

• Increased noise levels = decreased company loyalty

Unwanted sound negatively affects job performance, although performance levels are sometimes upheld at the price of increased stress. As noise levels increase, performance decreases.

Critical thinking is impaired and problem solving abilities diminish. Error rates increase, leading to workplace accidents and decreased profits. Ability to perform complex tasks diminishes. Degradation of working memory occurs. Auditory stressors increase norepinephrine and cortisol activities, negatively affecting cognitive performance.

Accidents and sick leave

Accidents are estimated to be as much a three to four times more prevalent in noisy environments.

Disruptive effects of noise are a contributing factor for increased risk of accidents. NIHL further increases one’s risk of having an accident. According to a recent study based on 240,000 person-years of observation, 12.2% of all occupational accidents are attributed to noise exposure above 90 dB(A), hearing loss or a combination thereof. The more severe the hearing loss, the greater the increase in the accident risk. Occupational noise exposure and NIHL negatively impact everyday safety in the workplace, resulting in loss of productivity and capital.

Absences attributed to compromised health status increase as noise exposure increases. Rising insurance premiums and compensation doled out for industrial injuries and sick leave can be quite costly.

Sound characteristics

Intensity, frequency, complexity, and duration of unwanted sound determine how it affects human wellbeing.

Subjective loudness increases at a slower rate than sound energy or sound pressure. Listeners judge the loudness as doubled only after an increase of 10 decibels (dB). Sound pressure levels (SPL) increase by 6 dB when sound pressure doubles. An increase of 20 dB results from multiplication of sound pressure by a factor of 10. Doubling sound energy only increases perceived loudness by 3 dB.

Exposure to almost all types of noise induces non-auditory effects. Intermittent noise impairs performance more than continuous noise. Sudden, intense noise precipitates cardiac dysrhythmias and increases catecholamine secretion, which in turn increases stress. Long term exposure to low frequency, large pressure amplitude noise (at or above 90 decibels and less than or equal to 500Hz) is thought to cause vibroacoustical disease. Highest percentages of tension, fatigue, and irritability result from noise exposure in the 86-90 dB(A) range.

Non auditory effects aren’t tabulated by summing accumulated sound energy. Dynamics detailing additive, interactive, or independent effects are not fully understood. Exposure may be augmented by a number of variables. The combination of noise plus another factor like vibration, ototoxic chemicals, or drugs, is additive and produces responses that are not possible by the individual factors. Few studies have encompassed two variables. Very little is known about how the effects of multiple variables sum up.

Sleep disturbances

Noise levels in the workplace can lead to sleep disturbances. When combined with shift work, the effects are additive. Lack of sleep negatively affects job performance.

Quiet periods away from the workplace are thought to facilitate physical recovery from daytime noise levels endured in the workplace. Sleep modulates cardiovascular function. Trouble falling asleep and sleep fragmentation could enable development of cardiovascular disorders.

Psychosocial effects

In one European Union survey, 28% of workers reported working conditions exposing them to noise loud enough that they had to raise their voices to communicate with co-workers at least 25% of the time. Inability to easily communicate with co-workers interferes in complex task performance. Social behaviour is impacted as a direct result of effects of noise on communication.

Communicating in a noisy environment above 55-60 dB(A) becomes increasingly difficult as noise level and workload increases and leads to increased irritability, annoyance, and feelings of isolation. Interaction with co-workers decreases.

An unwillingness to help one’s co-workers develops. Increased anger and aggression may lead to workplace violence.

Biochemical effects

The auditory system is our main sensory warning system, actively and continuously analysing, filtering, and interpreting acoustic information. Arousal of the autonomic nervous system (ANS) and endocrine system results from repeated temporal changes in biological responses. Chronic noise stress disrupts homeostasis. Prolonged stress reactions can be harmful to the human organism. Increased stress reactions increases catecholamine secretion which, in turn, leads to increased heart disease.

Among other non-auditory health endpoints, short term changes in circulation including blood pressure, heart rate, cardiac output and vasoconstriction, as well as stress hormones have been studied in experimental settings for many years.

Classical biological risk factors have been shown to be elevated in subjects that were exposed to high levels of noise. In the past several years, epidemiological evidence was accumulated supporting the hypothesis that persistent noise stress increases the risk of cardiovascular disorders including:

• Hypertension

• Heart Attack

• Cardiac Dysrhythmias

• Increased Heart Rate

• Peripheral Vasoconstriction/Vascular Resistance
Ischemic heart disease is the leading cause of death according to the 2000 WHO Global Burden of Disease Study. Increased evidence that noise affects health has sparked a growing interest in noise induced cardiovascular effects.

A question arises as to the magnitude of long term effects of noise exposure. Exposure-response relationships need more research in order to determine onset threshold and develop mitigation measures to intervene and decrease risk of adverse health outcomes.

Hearing protection

Hearing protectors not only protect hearing, they improve health and wellbeing. The best hearing protector is one employees actually use, and employees involved in selecting hearing protectors use them more often. Selection of hearing protectors must take compatibility with other PPE and workplace conditions such as temperature, pressure, and humidity into consideration.

According to the National Institute for Occupational Safety and Health (NIOSH), factors determining likelihood of worker acceptance include:

• Convenience and availability

• Belief that protectors can be worn correctly

• Belief that protectors will prevent hearing loss

• Belief that protectors will not impair one’s ability to hear important sounds

• Comfort/fit

• Adequate attenuation

• Compatibility with other required PPE

Offer a variety of types and styles and provide individual training on proper fit and use. Wearing hearing protectors correctly is of crucial importance. Intermittent wear will drastically reduce effective protection.

Many methods exist for estimating the amount of sound attenuation provided by hearing protectors. Most are based on laboratory data obtained using controlled conditions. Noise reduction actually experienced in the workplace can be significantly lower than ratings derived from laboratory data suggest.

Hearing protector ratings should be de-rated by a factor that correlates to real world data.


Reducing noise levels and limiting worker exposure to noise reduces or eliminates more health issues than just NIHL. It isn’t known how much noise reduction is required to eliminate non-auditory effects of noise in the workplace. Although it can be argued that evidence exists both for and against health effects, blood pressure and heart disease can be directly linked to noise exposure.

Typically, Hearing Conservation Plans do not effectively eliminate non-auditory health effects because they can occur at levels below hearing damage criterion. Implementation of an environmental noise management programme aimed at reducing noise at levels below hearing loss criterion, in conjunction with engineering controls and PPE, is imperative.

Additional research using improved methodology is needed. Understanding mechanisms and pathways is essential in preventing and reducing noise induced health effects.

Why wait for more studies, implement an environmental noise management programme aimed at reducing noise at levels lower than hearing loss criterion?

Decreased accidents are a very compelling argument for reducing noise in the workplace. Work related accidents result in significant capital and productivity losses for industry.

Immediate attention and action of all Health and Safety professionals is called for. The importance of recognising noise induced health effects, NIHL, or the combination of the two as risk factors for increased workplace accident rates is tremendous. 

Published: 01st Mar 2012 in OSA Magazine


Teresa A Long

Teresa A Long, Combustible Dust Policy Institute, Santa Fe, Texas, is dedicated to raising awareness of occupational health and safety hazards. Teresa served as the global focal point for reactor/train qualifications and FDA compliance audit programmes within the Polyolefins R&D characterisation group at Dow Chemical. Prior to that, Teresa performed analytical testing and method development while working at American Electric Power’s Dolan Engineering Laboratory. Teresa earned an AAS in Chemical Technology from Texas State Technical College in 2002 and a certificate in Environmental Health and Safety Technology (Applied Health Physics) in 2003. She is pursuing an Environmental Science degree at University of Houston-Clear Lake, majoring in Industrial Hygiene.


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